Estrogen, inflammation, and platelet phenotype

Sex dimorphisms in coagulation: Implications in trauma-induced coagulopathy and trauma resuscitation

Trauma-induced coagulopathy (TIC) is one of the leading causes of preventable death in injured patients. Consequently, it is imperative to understand the mechanisms underlying TIC and how to mitigate this mortality. An opportunity for advancement stems from the awareness that coagulation demonstrates a strong sex-dependent effect. Females exhibit a relative hypercoagulability compared to males, which persists after injury and confers improved outcomes. The mechanisms underlying sex dimorphisms in coagulation and its protective effect after injury have yet to be elucidated. This review explores sex dimorphisms in enzymatic hemostasis, fibrinogen, platelets, and fibrinolysis, with implications for resuscitation of patients with TIC.

Sex Differences in Culprit Plaque Characteristics Among Different Age Groups in Patients With Acute Coronary Syndromes

BACKGROUND

Despite the significant decline in cardiovascular mortality in women over the past several decades, sex differences in the underlying pathology of acute coronary syndromes remain poorly understood. Previous postmortem studies have demonstrated sex differences in coronary plaque morphology with a higher prevalence of plaque erosion in young women and more plaque rupture in older women after menopause, whereas men showed no increase in prevalence of plaque rupture with age. However, in vivo data are limited.

METHODS

This study included patients who presented with acute coronary syndrome and underwent preintervention optical coherence tomography imaging of the culprit lesion. The culprit plaque was categorized as plaque rupture, plaque erosion or culprit plaque with calcification, and stratified by age. Features of plaque vulnerability at culprit lesion were also analyzed.

RESULTS

In 1368 patients (women=286), women and men had a similar distribution of culprit plaque morphology (plaque rupture versus plaque erosion). However, significant sex differences were found in the underlying mechanisms of acute coronary syndrome among different age groups: women showed a significant ascending trend with age in plaque rupture (P<0.001) and the features of plaque vulnerability such as lipid plaque (P<0.001), thin-cap fibroatheroma (P=0.005), and microstructures including macrophages, cholesterol crystals, and calcification (P=0.026). No trend was observed in men.

CONCLUSIONS

Age related sex differences in culprit plaque morphology and vulnerability were identified in patients with acute coronary syndrome: prevalence of plaque rupture and vulnerability increased with age in women but not in men.

REGISTRATION

URL: https://www.

CLINICALTRIALS

gov; Unique identifier: NCT01110538 and NCT03479723.

Effect of menopausal hormone therapy on proteins associated with senescence and inflammation

BACKGROUND

Estrogen may inhibit cell senescence that contributes to age-related disorders. This study determined the effects of menopausal hormone treatments on circulating levels of markers of cell senescence.

METHODS

Growth differentiation factor 15 (GDF15), tumor necrosis factor receptor 1 (TNFR1), FAS, and macrophage inflammatory protein 1α (MIP1α) were measured in serum using multiplexed bead-based assays and compared among menopausal women participating in the Kronos Early Estrogen Prevention Study randomized to either placebo (n = 38), oral conjugated equine estrogen (oCEE, n = 37), or transdermal 17β-estradiol (tE2, n = 34). Serum levels of the senescent markers for each treatment were compared to placebo 36 months after randomization using the Wilcoxon rank sum test.

RESULTS

Serum levels of GDF15, TNFR1, and FAS, but not MIP1α, were lower in both the oCEE and tE2 groups compared to placebo. The difference in levels between treatment and placebo for GDF15, TNFR1, and FAS were greater for oCEE [-108 pg/mL (p = .008), -234 pg/mL (p = .0006), and -1374 pg/mL (p < .0001), respectively] than for tE2 [-76 pg/mL (p = .072), -105 pg/mL (p = .076), and -695 pg/mL (p = .036), respectively]. Additionally, TNFR1 showed a positive association with time past menopause (correlation = 0.255, p = .019).

CONCLUSIONS

Circulating levels of some markers of cell senescence were lower in menopausal women treated with oCEE and tE2 compared to placebo. Differences in the magnitude of effect of the two active treatments may reflect the differences in circulating levels of estrogen metabolites due to formulation and mode of delivery. These data generate new hypotheses with regard to the effects of menopause on the biology of aging.

Aerobic exercise training lowers platelet reactivity and improves platelet sensitivity to prostacyclin in pre- and postmenopausal women

Essentials It is unknown how regular exercise affects platelet function after menopause. We studied the effect of 3-months of high-intensity exercise in pre- and postmenopausal women. Platelet sensitivity to the inhibitory effect of arterially infused prostacyclin was increased. Reduced basal platelet reactivity was seen in the premenopausal women only.

SUMMARY

Background The risk of atherothrombotic events increases after the menopause. Regular physical activity has been shown to reduce platelet reactivity in younger women, but it is unknown how regular exercise affects platelet function after the menopause. Objectives To examine the effects of regular aerobic exercise in late premenopausal and recent postmenopausal women by testing basal platelet reactivity and platelet sensitivity to prostacyclin and nitric oxide. Methods Twenty-five sedentary, but healthy, late premenopausal and 24 matched recently postmenopausal women, mean (95% confidence interval) 49.1 (48.2-49.9) and 53.7 (52.5-55.0) years old, participated in an intervention study: 3-month high-intensity supervised aerobic spinning-cycle training (1 h, × 3/week). Basal platelet reactivity was analyzed in platelet-rich plasma from venous blood as agonist-induced % aggregation. In a subgroup of 13 premenopausal and 14 postmenopausal women, platelet reactivity was tested ex vivo after femoral arterial infusion of prostacyclin, acetylcholine, a cyclooxygenase inhibitor, and after acute one-leg knee extensor exercise. Results Basal platelet reactivity (%aggregation) to TRAP-6 (1 μm) was higher in the postmenopausal, 59% (50-68), than the premenopausal women, 45% (35-55). Exercise training reduced basal platelet reactivity to collagen (1 μg mL-1 ) in the premenopausal women only: from 63% (55-71%) to 51% (41-62%). After the training intervention, platelet aggregation was more inhibited by the arterial prostacyclin infusion and the acute exercise in both premenopausal and postmenopausal women. Conclusions These results highlight previously unknown cardioprotective aspects of regular aerobic exercise in premenopausal and postmenopausal women, improving their regulation of platelet reactivity through an increased platelet sensitivity to prostacyclin, which may counterbalance the increased atherothrombotic risk associated with the menopause.

Pregnancy history and blood-borne microvesicles in middle aged women with and without coronary artery calcification

BACKGROUND AND AIMS

Having a history of preeclampsia increases the risk for future coronary artery calcification (CAC). This study evaluated the association of blood-borne, cell-derived microvesicles (MV) with CAC in middle-aged women.

METHODS

Twelve pre-selected, antigen-specific MV were measured by digital flow cytometry in the blood of age- and parity-matched women (median age 60 years) without a history of cardiovascular events, but with either a history of preeclampsia (PE, n = 39) or normotensive pregnancy (NP, n = 40). CAC was determined by computed tomography.

RESULTS

CAC scores ranged from 0 to 47 and 0-602 Agatston Units in the NP and PE groups, respectively. Waist circumference and insulin resistance were greatest in PE women with CAC. MV positive for tissue factor or stem/progenitor cell antigen (CD117) differed between NP and PE groups. In univariate analysis, those positive for tissue factor, ICAM-1, stem cells, and adipocytes (P16-set) antigens associated with CAC in the PE group. Principal components (PC) analysis reduced the MV variables to three independent dimensions. PC1 showed a modest correlation with CAC scores in the PE group (ρ = 0.31, p = 0.06) and associated with CAC in a multivariable model on pooled groups that included all 3 PC variables when adjusted for pregnancy status (p = 0.03). The association was lost when corrected for body mass index or waist circumference.

CONCLUSIONS

In women with a history of PE and elevated metabolic risk profile, a group of specific antigen-positive MV associated with CAC. These MV may reflect cellular processes associated with CAC. Their diagnostic potential for CAC remains to be determined.

Gender Differences in Cardiovascular Drugs

The different responses of women and men to cardiovascular drugs reflect gender -specific variances in pharmacokinetic profiles and drug sensitivities coupled to inherent differences in the underlying physiology of each sex. Thus, many common cardiovascular drugs exhibit gender -specific therapeutic and adverse effects. For example, the QT interval of the electrocardiogram is longer in women compared to men, and accordingly, drugs that prolong the QT interval are more likely to cause lethal ventricular arrhythmias in female than male patients. As more clinical drug trials include women subjects, our improved knowledge base for assessing the risk/benefit ratio for cardiovascular drugs in women will enable us to consider gender as one factor in prescribing drugs and adjusting drug loading and maintenance dosages. This short review will present evidence for gender- related differences in the responses to common cardiovascular drugs including statins, antiplatelet and antithrombotic agents, β-blockers, digoxin, vasodilator therapies, and drugs associated with the Long QT Syndrome.

Specific cell-derived microvesicles: Linking endothelial function to carotid artery intima-media thickness in low cardiovascular risk menopausal women

BACKGROUND

Decreases in endothelial function measured by reactive hyperemic index (RHI) correlated with increases in carotid intima-media thickness (CIMT) in recently menopausal women with a low risk cardiovascular profile. Factors linking this association are unknown.

OBJECTIVE

Assess, longitudinally, markers of platelet activation and cell-derived, blood-borne microvesicles (MV) in relationship to RHI and CIMT in asymptomatic, low risk menopausal women.

METHODS

RHI by digital pulse tonometry (n = 93), CIMT by ultrasound (n = 113), measures of platelet activation and specific cell-derived, blood-borne MV were evaluated in women throughout the Kronos Early Estrogen Prevention Study (KEEPS) at Mayo Clinic.

RESULTS

CIMT, but not RHI, increased significantly over 4 years. The average change in CIMT correlated significantly with the average follow-up values of MV positive for common leukocyte antigen [CD45; ρ = 0.285 (P = 0.002)] and VCAM-1 [ρ = 0.270 (P = 0.0040)]. Using principal components analysis (PC) on the aggregate set of average follow-up measures, the first derived PC representing numbers of MV positive for markers of vascular endothelium, inflammatory cells (leukocyte and monocytes), pro-coagulant (tissue factor), and cell adhesion molecules (ICAM-1 and VCAM-1) associated with changes in RHI and CIMT. Changes in RHI associated with another PC defined by measures of platelet activation (dense granular ATP secretion, surface expression of P-selectin and fibrinogen receptors).

CONCLUSIONS

MV derived from activated endothelial and inflammatory cells, and those expressing cell adhesion and pro-coagulant molecules may reflect early vascular dysfunction in low risk menopausal women. Assays of MV as non-conventional measures to assess cardiovascular risk in asymptomatic women remain to be developed.

Congress on women's health Trudy Bush lecture 2014: new insights into sex Hormones and Cardiovascular disease

Many basic, mechanistic studies of how sex steroids alter vascular function proceeded from Dr. Bush's seminal epidemiologic observations that noncontraceptive use of estrogen reduced all-cause and cardiovascular mortality. However, translating findings from these basic science studies into clinical trials and clinical guidelines has been controversial. This commentary reviews the development of sex steroid vascular research, identifies mechanisms by which sex steroids affect vascular function, reviews findings from recent clinical hormone trials, and identifies challenges and the need for continued funding of such investigations.

Pharmacogenomics, pharmacokinetics and pharmacodynamics: interaction with biological differences between men and women

Pharmacological response depends on multiple factors and one of them is sex-gender. Data on the specific effects of sex-gender on pharmacokinetics, as well as the safety and efficacy of numerous medications, are beginning to emerge. Nevertheless, the recruitment of women for clinical research is inadequate, especially during the first phases. In general, pharmacokinetic differences between males and females are more numerous and consistent than disparities in pharmacodynamics. However, sex-gender pharmacodynamic differences are now increasingly being identified at the molecular level. It is now even becoming apparent that sex-gender influences pharmacogenomics and pharmacogenetics. Sex-related differences have been reported for several parameters, and it is consistently shown that women have a worse safety profile, with drug adverse reactions being more frequent and severe in women than in men. Overall, the pharmacological status of women is less well studied than that of men and deserves much more attention. The design of clinical and preclinical studies should have a sex-gender-based approach with the aim of tailoring therapies to an individual's needs and concerns.

Thrombogenic microvesicles and white matter hyperintensities in postmenopausal women

OBJECTIVE

To determine the association of conventional cardiovascular risk factors, markers of platelet activation, and thrombogenic blood-borne microvesicles with white matter hyperintensity (WMH) load and progression in recently menopausal women.

METHODS

Women (n = 95) enrolled in the Mayo Clinic Kronos Early Estrogen Prevention Study underwent MRI at baseline and at 18, 36, and 48 months after randomization to hormone treatments. Conventional cardiovascular risk factors, carotid intima-medial thickness, coronary arterial calcification, plasma lipids, markers of platelet activation, and thrombogenic microvesicles were measured at baseline. WMH volumes were calculated using a semiautomated segmentation algorithm based on fluid-attenuated inversion recovery MRI. Correlations of those parameters with baseline WMH and longitudinal change in WMH were adjusted for age, months past menopause, and APOE ε4 status in linear regression analysis.

RESULTS

At baseline, WMH were present in all women. The WMH to white matter volume fraction at baseline was 0.88% (0.69%, 1.16%). WMH volume increased by 122.1 mm(3) (95% confidence interval: -164.3, 539.5) at 36 months (p = 0.003) and 155.4 mm(3) (95% confidence interval: -92.13, 599.4) at 48 months (p < 0.001). These increases correlated with numbers of platelet-derived and total thrombogenic microvesicles at baseline (p = 0.03).

CONCLUSION

Associations of platelet-derived, thrombogenic microvesicles at baseline and increases in WMH suggest that in vivo platelet activation may contribute to a cascade of events leading to development of WMH in recently menopausal women.

Microvesicles at the crossroads between infection and cardiovascular diseases

Observational and experimental studies continue to support the association of infection and infection-stimulated inflammation with development of cardiovascular disease (CVD) including atherosclerosis and thrombosis. Microvesicles (MV) are heterogeneous populations of sealed membrane-derived vesicles shed into circulation by activated mammalian cells and/or pathogenic microbes that may represent an interface between bacterial/microbial infection and increased risk of CVD. This review evaluates how MV act to modulate and intersect immunological and inflammatory responses to infection with particular attention to progression of CVD. Although infection-related stimuli provoke release of MV from blood and vascular cells, MV express phosphatidylserine and other procoagulant factors on their surface, which initiate and amplify blood coagulation. In addition, MV mediate cell-cell adhesion, which may stimulate production of pro-inflammatory cytokines in vascular cells, which in turn aggravate progression of CVD and propagate atherothrombosis. MV transfer membrane receptors, RNA and proteins among cells, and present auto-antigens from their cells of origin to proximal or remote target cells. Because MV harbor cell surface proteins and contain cytoplasmic components of the parent cell, they mediate biological messages and play a pivotal role in the crossroad between infection-stimulated inflammation and CVDs.

Strategies and methods to study sex differences in cardiovascular structure and function: a guide for basic scientists

Background

Cardiovascular disease remains the primary cause of death worldwide. In the US, deaths due to cardiovascular disease for women exceed those of men. While cultural and psychosocial factors such as education, economic status, marital status and access to healthcare contribute to sex differences in adverse outcomes, physiological and molecular bases of differences between women and men that contribute to development of cardiovascular disease and response to therapy remain underexplored.

Methods

This article describes concepts, methods and procedures to assist in the design of animal and tissue/cell based studies of sex differences in cardiovascular structure, function and models of disease.

Results

To address knowledge gaps, study designs must incorporate appropriate experimental material including species/strain characteristics, sex and hormonal status. Determining whether a sex difference exists in a trait must take into account the reproductive status and history of the animal including those used for tissue (cell) harvest, such as the presence of gonadal steroids at the time of testing, during development or number of pregnancies. When selecting the type of experimental animal, additional consideration should be given to diet requirements (soy or plant based influencing consumption of phytoestrogen), lifespan, frequency of estrous cycle in females, and ability to investigate developmental or environmental components of disease modulation. Stress imposed by disruption of sleep/wake cycles, patterns of social interaction (or degree of social isolation), or handling may influence adrenal hormones that interact with pathways activated by the sex steroid hormones. Care must be given to selection of hormonal treatment and route of administration.

Conclusions

Accounting for sex in the design and interpretation of studies including pharmacological effects of drugs is essential to increase the foundation of basic knowledge upon which to build translational approaches to prevent, diagnose and treat cardiovascular diseases in humans.

Sex differences in antiplatelet response in ischemic stroke

Sex differences exist in the occurrence, treatment and outcome of ischemic stroke. Compared with men, women have more stroke events and are less likely to fully recover from a stroke. Given the rapidly aging population, stroke incidence and mortality among women are projected to substantially rise by 2050. This has important public health consequences. Mitigating the burden of stroke among women will require a fundamental understanding of sex differences and sex-specific issues including cerebrovascular disease pathophysiology, treatment and outcome. An aspect of stroke treatment receiving increasing but insufficient attention involves possible interactions between estrogen levels, antiplatelet drugs and stroke outcome. Emerging evidence suggests that antiplatelet therapy may provide primary stroke protection but not primary myocardial infarction prevention in women, while the opposite may be true among men. Understanding sex-specific issues related to women who experience stroke is critical to clinicians who treat women with antiplatelet medications as part of a secondary stroke prevention regimen; however, the ideal antiplatelet medication, and dose, in women requires further research. In this article we present a conceptual framework for sex differences in antiplatelet treatment response in ischemic stroke, thrombus formation and the mediating role of estrogen, sex differences in antiplatelet treatment response in clinical trials, and sex differences in antiplatelet treatment use in ischemic stroke.

Serotonin, depression, and cardiovascular disease: sex-specific issues

The comorbidity of cardiovascular disease (CVD) and depression/anxiety disorders is well established, but the mechanisms are not well understood. This paper will review the epidemiological and biological evidence for the role of depression in CVD, as well as the pathophysiological process underlying both depression and CVD. The focus will be on the roles of serotonin, platelets, and the immune system, with an emphasis on the relevance of sex differences in both depression/anxiety and CVD as they pertain to women.

Alterations in platelet function and cell-derived microvesicles in recently menopausal women: relationship to metabolic syndrome and atherogenic risk

A woman's risk for metabolic syndrome (MS) increases at menopause, with an associated increase in risk for cardiovascular disease. We hypothesized that early menopause-related changes in platelet activity and concentrations of microvesicles derived from activated blood and vascular cells provide a mechanistic link to the early atherothrombotic process. Thus, platelet functions and cellular origin of blood-borne microvesicles in recently menopausal women (n = 118) enrolled in the Kronos Early Estrogen Prevention Study were correlated with components of MS and noninvasive measures of cardiovascular disease [carotid artery intima medial thickness (CIMT), coronary artery calcium (CAC) score, and endothelial reactive hyperemic index (RHI)]. Specific to individual components of the MS pentad, platelet number increased with increasing waist circumference, and platelet secretion of ATP and expression of P-selectin decreased with increasing blood glucose (p = 0.005) and blood pressure (p < 0.05), respectively. Waist circumference and systolic blood pressure were independently associated with monocyte- and endothelium-derived microvesicles (p < 0.05). Platelet-derived and total procoagulant phosphatidylserine-positive microvesicles, and systolic blood pressure correlated with CIMT (p < 0.05), but not with CAC or RHI. In summary, among recently menopausal women, specific platelet functions and concentrations of circulating activated cell membrane-derived procoagulant microvesicles change with individual components of MS. These cellular changes may explain in part how menopause contributes to MS and, eventually, to cardiovascular disease.

The platelet as a model system for the acute actions of nuclear receptors

Platelets are circulating cell fragments which play a critical role in thrombosis, and whose activity is associated with the progress of cardiovascular diseases, diabetes, inflammation, and cancer cell metastasis. Recently, a number of nuclear receptors have been found present in human platelets, including the receptors for sex steroids, and glucocorticoids, along with peroxisome proliferator-activated receptors (PPAR)s and retinoid X receptors (RXR)s. Although the platelet contains no nucleus, selective ligands for these receptors activate their respective platelet nuclear receptors and regulate platelet aggregation and activation. The human platelet, because of its abundance and accessibility therefore represents an excellent model system to study the rapid non-genomic mechanism of nuclear receptors. Moreover, since targeting platelets is a major clinical therapeutic area, analysis of platelet nuclear receptors may provide clues for new drug targets as well as provide important information regarding the physiological roles of nuclear receptors in the circulation.

Estrogen receptor interactions and dynamics monitored in live cells by fluorescence cross-correlation spectroscopy

Quantitative characterization of protein interactions in live cells remains one of the most important challenges in modern biology. In the present work we have used two-photon, two-color, fluorescence cross-correlation spectroscopy (FCCS) in transiently transfected COS-7 cells to measure the concentrations and interactions of estrogen receptor (ER) subtypes alpha and beta with one of their transcriptional coactivator proteins, TIF2, as well as heterodimerization between the two ER subtypes. Using this approach in a systematic fashion, we observed a strong ligand-dependent modulation of receptor-coactivator complexation, as well as strong protein concentration dependence for complex formation in the absence of ligand. These quantitative values for protein and complex concentrations provide the first estimates for the ER-TIF2 K(d) for the full-length proteins and in a cellular context (agonist, < approximately 6 nM; antagonist, > approximately 3 microM; unliganded, approximately 200 nM). Coexpression of the two ER subtypes revealed substantial receptor heterodimer formation. They also provide, for the first time, estimated homo- and heterodimerization constants found to be similar and in the low nanomolar range. These results underscore the importance of receptor and coregulator expression levels and stability in the tissue-dependent modulation of receptor function under normal and pathological conditions.

Platelets and innate immunity

Although platelets are best known as primary mediators of hemostasis, this function intimately associates them with inflammatory processes, and it has been increasingly recognized that platelets play an active role in both innate and adaptive immunity. For example, platelet adhesive interactions with leukocytes and endothelial cells via P-selectin can lead to several pro-inflammatory events, including leukocyte rolling and activation, production of cytokine cascades, and recruitment of the leukocytes to sites of tissue damage. Superimposed on this, platelets express immunologically-related molecules such as CD40L and Toll-like receptors that have been shown to functionally modulate innate immunity. Furthermore, platelets themselves can interact with microorganisms, and several viruses have been shown to cross-react immunologically with platelet antigens. This review discusses the central role that platelets play in inflammation, linking them with varied pathological conditions, such as atherosclerosis, sepsis, and immune thrombocytopenic purpura, and suggests that platelets also act as primary mediators of our innate defences.

Aggregation and microparticle production through toll-like receptor 4 activation in platelets from recently menopausal women

Bacterial infection may increase risk for thrombosis and atherosclerosis. Human platelets express toll-like receptor 4 (TLR4), the receptor for gram-negative bacterial lipopolysaccharide (LPS). Experiments were designed to evaluate direct, acute effects of TLR4 activation on aggregation, secretion, and generation of prothrombogenic microparticles in vitro on platelets derived from healthy women at risk for development of cardiovascular disease because of their hormonal status. Platelet-rich plasma from recently menopausal women was incubated with ultrapure Escherichia coli LPS in the absence or presence of antibodies that neutralize the human TLR4. Incubating platelets with LPS (100 ng/mL) for 5 minutes decreased aggregation and dense granule adenosine triphosphate secretion induced by thrombin receptor agonist peptide (TRAP) but not by adenosine diphosphate or collagen. The antibody to TLR4 blocked this effect of LPS. TLR4 activation increased phosphorylation of p38 mitogen-activated protein kinase and decreased production of prothrombotic phosphatidylserine and P-selectin-positive microparticles in response to TRAP. Therefore, acute, direct activation of TLR4 reduces platelet reactivity to TRAP stimulation in vitro. Increased thrombotic and cardiovascular risk with bacterial infection most likely reflects the sum of TLR4 activation on other blood and vascular cells to release proinflammatory cytokines/chemokines, which indirectly affect platelet reactivity.

Circulating microparticles and endogenous estrogen in newly menopausal women

BACKGROUND

Estrogen modulates antithrombotic characteristics of the vascular endothelium and the interaction of blood elements with the vascular surface. A marker of these modulatory activities is formation of cell-specific microparticles. This study examined the relationship between blood-borne microparticles and endogenous estrogen at menopause.

METHODS

Platelet activation and plasma microparticles were characterized from women being screened (n = 146) for the Kronos Early Estrogen Prevention Study. Women were grouped according to serum estrogen (< 20 pg/ml; low estrogen, n = 21 or > 40 pg/ml; high estrogen, n = 11).

RESULTS

Age, body mass index, blood pressure and blood chemistries were the same in both groups. No woman was hypertensive, diabetic or a current smoker. Platelet counts, basal and activated expression of P-selectin on platelet membranes were the same, but activated expression of glycoprotein IIb/IIIa was greater in the high-estrogen group. Numbers of endothelium-, platelet-, monocyte- and granulocyte-derived microparticles were greater in the low-estrogen group. Of the total numbers of microparticles, those positive for phosphatidylserine and tissue factor were also greater in the low-estrogen group.

CONCLUSION

These results suggest that, with declines in endogenous estrogen at menopause, numbers of procoagulant microparticles increase and thus may provide a means to explore mechanisms for cardiovascular risk development in newly menopausal women.

Effect of ovariectomy on blood pressure and venous tone in female spontaneously hypertensive rats

BACKGROUND

Venous capacitance plays an important role in circulatory homeostasis. A number of reports have suggested an effect of estrogen on venous function. This study tested the hypothesis that ovariectomy would increase venous tone in the female spontaneously hypertensive rat (SHR) via autonomic mechanisms.

METHODS

Five-week-old female SHR were subjected to sham operation (Sham) or ovariectomy (OVX). At 10 weeks of age, the rats were instrumented for the measurement of arterial and venous pressure. A balloon catheter was advanced into the right atrium. Mean circulatory filling pressure (MCFP), an index of venous tone, was calculated. Mean arterial pressure (MAP), heart rate (HR), and MCFP were recorded from conscious rats. Postsynaptic adrenergic responsiveness was assessed by constructing cumulative dose-response curves to norepinephrine (NE).

RESULTS

MAP was not significantly affected by ovariectomy (Sham 127 +/- 6 mm Hg vs. OVX 130 +/- 3 mm Hg). HR also was not different between groups (Sham 409 +/- 11 bpm vs. OVX 399 +/- 12 bpm). Conversely, MCFP was significantly, but moderately, increased in OVX SHR (Sham 5.2 +/- 0.2 mm Hg vs. OVX 5.9 +/- 0.2 mm Hg). Ganglionic blockade produced marked decreases in MAP, HR, and MCFP in both groups; however, the responses were not different between groups. Infusion of NE caused dose-dependent increases in MAP and MCFP. There were no statistically significant differences in these responses between Sham and OVX SHR.

CONCLUSION

Endogenous ovarian hormones effect a small reduction in MCFP. This effect does not appear to be mediated by adrenergic mechanisms.

Vascular actions of estrogens: functional implications

The impact of estrogen exposure in preventing or treating cardiovascular disease is controversial. But it is clear that estrogen has important effects on vascular physiology and pathophysiology, with potential therapeutic implications. Therefore, the goal of this review is to summarize, using an integrated approach, current knowledge of the vascular effects of estrogen, both in humans and in experimental animals. Aspects of estrogen synthesis and receptors, as well as general mechanisms of estrogenic action are reviewed with an emphasis on issues particularly relevant to the vascular system. Recent understanding of the impact of estrogen on mitochondrial function suggests that the longer lifespan of women compared with men may depend in part on the ability of estrogen to decrease production of reactive oxygen species in mitochondria. Mechanisms by which estrogen increases endothelial vasodilator function, promotes angiogenesis, and modulates autonomic function are summarized. Key aspects of the relevant pathophysiology of inflammation, atherosclerosis, stroke, migraine, and thrombosis are reviewed concerning current knowledge of estrogenic effects. A number of emerging concepts are addressed throughout. These include the importance of estrogenic formulation and route of administration and the impact of genetic polymorphisms, either in estrogen receptors or in enzymes responsible for estrogen metabolism, on responsiveness to hormone treatment. The importance of local metabolism of estrogenic precursors and the impact of timing for initiation of treatment and its duration are also considered. Although consensus opinions are emphasized, controversial views are presented to stimulate future research.